Assembly for use with a return to neutral mechanism

ABSTRACT

A control assembly for use with hydraulic apparatus having a housing, a trunnion extending from the housing, a return arm and a control arm mounted on the trunnion. The control assembly is attached to the trunnion arm and includes a pair of scissor return arms biased to place the hydraulic apparatus in a neutral condition, a pair of bushings and a spacer pressed into the bushings to form the assembly.

BACKGROUND OF THE INVENTION

This invention relates generally to an axle driving apparatus and, more particularly, to an assembly used in connection with a return to neutral mechanism adapted to be mounted to the housing of a hydraulic drive apparatus such as an integrated hydrostatic transaxle (“IHT”) or hydrostatic transmission (“HST”). The mechanism disclosed herein could also be used with hydraulic pumps or other types of hydrostatic transaxles.

The general design of IHTs and HSTs are known in the art and generally include a rotating hydraulic pump and a rotating hydraulic motor, carrying a plurality of reciprocating pistons which are in fluid communication through hydraulic porting. Rotation of the hydraulic pump against a moveable swash plate creates an axial motion of the pump pistons that forces an operating oil through the hydraulic porting to the hydraulic motor to move the motor pistons and cause rotation of the hydraulic motor to drive an output shaft or axle.

The swash plate position is adjustable to vary the speed and direction of rotation of the hydraulic motor and, accordingly, the speed and direction of the output rotation. For use in changing the position of the moveable swash plate, it is known to include a trunnion arm coupled to the swash plate. A speed change lever or a speed change pedal is, in turn, coupled to the trunnion arm through a wire or other driving link. In this manner, movement of the speed change lever/pedal results in movement of the trunnion arm to change the position of the swash plate to thereby control the speed and direction of the vehicle. An example of such a mechanism for adjusting the speed of a vehicle may be seen in commonly owned U.S. Pat. No. 6,122,996 which is incorporated herein by reference in its entirety.

For placing the swash plate in a position that neither affects the speed nor the direction of rotation of the hydraulic motor, i.e., the neutral position, a return to neutral mechanism is normally implemented as an integral part of the vehicle linkage. One known return to neutral mechanism is shown in commonly owned U.S. Pat. No. 6,782,797, the terms of which are incorporated herein by reference. Such a speed adjusting mechanism includes a return arm adapted to be mounted to casing in a fixed position indicative of a neutral position of the trunnion arm and a control arm that is mounted to and moves the trunnion arm. A pair of scissor return arms move the control arm in cooperation with the return arm for the purpose of moving the trunnion arm to the neutral position.

SUMMARY OF THE INVENTION

The invention disclosed herein comprises an assembly for use in connection with a return to neutral control mechanism for a transaxle or the like, whereby certain components of the mechanism may be preassembled, thereby increasing the ease of assembly of the entire unit and decreasing assembly costs.

A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth an illustrative embodiment and which are indicative of the various ways in which the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an embodiment of a speed adjusting mechanism including a control assembly in accordance with the present invention.

FIG. 2 is an exploded perspective view of a subassembly of the speed adjusting mechanism shown in FIG. 1.

FIG. 3 is a cross-sectional view of the subassembly of the speed adjusting mechanism shown in FIGS. 1 and 2.

FIG. 4 is a cross-sectional view of an alternative embodiment of the subassembly of the speed adjusting mechanism.

FIG. 5 is an exploded view of a further alternative embodiment of the subassembly of the speed adjusting mechanism.

FIG. 6 is a cross-sectional view of the subassembly of the speed adjusting mechanism shown in FIG. 5, shown with other control elements.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now to the figures, wherein like reference numerals refer to like elements, the present invention is depicted as used in connection with transaxle 10, which may be substantially identical to that described in commonly owned U.S. Pat. No. 6,152,247, which is incorporated herein by reference in its entirety. The details of transaxle 10 are not critical to this invention and will not be described in detail herein; this invention could also be used on other transaxle or transmission designs and this disclosure should not be read as limited to use with a zero-turn transaxle such as transaxle 10. The return to neutral design depicted herein is similar in many respects to that shown in U.S. Pat. No. 6,782,797; it will be understood that the assembly of the present invention may be used in connection with other designs and that this invention is not so limited. For further details on the operation of transaxle 10 or the return to neutral feature, the reader is referred to the patents referenced above.

The only element of the internal functioning of transaxle 10 that is key to this invention and thus depicted in the figures is trunnion 14, which extends from casing 11 and, it will be understood, is connected to a moveable swash plate (not shown) or similar structure. As will be understood by those of ordinary skill in the art, the swash plate may be moved to a variety of positions to vary the stroke of the pump pistons and the direction of rotation of the hydraulic motor. As the stroke of the pump pistons is varied, the volume of the hydraulic fluid pumped into the hydraulic porting of the center section will vary. Since the speed of rotation of the hydraulic motor is dependent upon the amount of hydraulic fluid pumped thereinto by the hydraulic pump and the direction of rotation of the hydraulic motor is dependent upon the direction of rotation of the hydraulic pump, the positioning of the swash plate is seen to control the speed and direction of rotation of the hydraulic motor and, accordingly, the speed and direction of rotation of an output or axle shaft.

To rotate trunnion arm 14 and, accordingly, move the swash plate assembly, a speed adjusting mechanism 316 is coupled to trunnion arm 14. Speed adjusting mechanism 316 may be connected, via a driving link, to a lever or pedal (not shown) provided on a vehicle (not shown) whereby movement of the lever or pedal is translated to the speed adjusting mechanism 316 to cause the rotation of trunnion arm 14 and movement of the swash plate assembly. Seal 30 is used to prevent leakage of hydraulic fluid from the opening in casing 11 from which trunnion arm 14 extends.

As shown in FIGS. 1 and 2, speed adjusting mechanism 316 is comprised of a return arm 20, a control arm 22, an inner scissor return arm 324, and an outer scissor return arm 326. A nut 34, which would be mated with corresponding threads on the end of trunnion arm 14, retains speed adjusting mechanism 316 on trunnion arm 14. Speed adjusting mechanism 316 also functions to substantially establish the neutral position of trunnion arm 14, i.e., the position of trunnion arm 14 where the swash plate assembly does not influence the flow of hydraulic fluid within the hydraulic circuit, and to bias and move trunnion arm 14 towards this neutral position.

Control arm 22 is non-rotatably mounted to the end of trunnion arm 14, preferably by providing control arm 22 and trunnion arm 14 with complimentary mating shapes, so that rotation of control arm 22 will also result in rotation of trunnion arm 14. Control arm 22 includes openings 22 c to which a driving link may be attached. A biasing means such as spring 36 is linked to inner and outer scissor return arms 324 and 326, and in particular, to arms 324 b and 326 b, respectively.

When trunnion arm 14 is placed in the position that corresponds to the neutral position of the swash plate, return arm 20 is attached to casing 11. For this purpose, an attachment device 32, such as a bolt/washer combination or the like, is inserted through an opening 20 b and mated with casing 11 to trap return arm 20 between attachment device 32 and casing 11 and frictionally prevent return arm 20 from moving. At this time, under the influence of biasing means 36, projection 22 a of control arm 22 and projection 20 a of return arm 20 will be in alignment. This alignment of the projections 22 a and 20 a establishes the neutral position. In the neutral position, both inner scissor return arm 324 and outer scissor return arm 326 are in contact with projection 22 a.

When speed adjusting mechanism 316 is rotated in a first direction, projection 22 a of control arm 22 will contact arm 324 a of inner scissor return arm 324, resulting in the movement of inner scissor return arm 324. Meanwhile, arm 326 a of outer scissor return arm 326 is prevented from moving as it remains in contact with projection 20 a of return arm 20. When speed adjusting mechanism 316 is rotated in the opposite direction, projection 22 a of control arm 22 will contact the arm 326 a of outer scissor return arm 326, resulting in the movement of outer scissor return arm 326. Meanwhile, arm 324 a of inner scissor return arm 324 is prevented from moving as it remains in contact with the projection 20 a of return arm 20. In either case, once the force from the driving link is no longer applied to control arm 22, spring 36 will cause the scissor return arm that has been rotated to move towards the other scissor return arm that has been held in place, thus returning trunnion arm 14 to the neutral position.

Because such return to neutral mechanisms comprise a plurality of components, it is advantageous to preassemble a portion of the return to neutral mechanism in order to simplify assembly and reduce costs. Assembly 300 is shown in FIGS. 1 and 2 as part of speed adjusting mechanism 316. Assembly 300 is formed of inner arm 324, outer arm 326, spacer 344, a pair of bushings 350 and an optional washer 342. Bushings 350 are preferably identical, and each comprise a main flange and a generally tubular portion 350 a that extends into an opening in the respective arms 324, 326. Spacer 344 is pressed into the tubular portions 350 a of both bushings 350, and the components are retained in place by the frictional contact between the components. The advantage of this configuration will be obvious from the following discussion.

Assembly 300 is formed by capturing arm 324, washer 342, and arm 326 between the two bushings 350, as shown particularly in FIGS. 2 and 3, with the bushings 350 being located on opposite sides of the assembly. Spacer 344 is pressed into the two bushings 350 to hold the assembly together by the contact between these components. Thus, the contact between spacer 344 and the two bushings 350 serves to hold all of the components of assembly 300 together so that they may be attached to other elements of a transaxle as a single assembly. Once assembly 300 is formed, there is sufficient space between the two bushings 350 to encourage free rotational movement of inner arm 324 and outer arm 326 with respect to one another. The use of this separate subassembly greatly simplifies the assembly of the entire return to neutral assembly and the transaxle.

In some circumstances it may be desirable to move the junction between the bushings away from washer 342. FIG. 4 shows an alternative embodiment, and in particular assembly 301 including bushings 341 and 343. The internal portion 341 a of bushing 341 is slightly longer than internal portion 343 a of bushing 343 so that the location where bushings 341 and 343 meet is not directly under washer 342. This configuration assists in keeping washer 342 in full contact with the periphery of internal portion 341 a of bushing 341 rather than the junction of bushings 341 and 343.

FIGS. 5 and 6 show yet another embodiment in the form of assembly 400, which is similar in many respects to assembly 300 and assembly 301. However, bushing 443 has a tab 443 a that engages an interlocking feature, such as step area 441 a, on bushing 441, so that bushings 441 and 443 are physically secured to one another, thus increasing the integrity of assembly 400 in comparison to assemblies 300 and 301. Spacer 444 in this configuration is also slightly different from previous spacers disclosed herein. However, spacer 444 serves a similar function to previously disclosed spacer embodiments.

While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangement disclosed is meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any equivalents thereof. 

1. An assembly for use in connection with a return to neutral mechanism on a hydraulic drive apparatus, the assembly comprising: a first and a second scissor return arm; a first bushing located on one side of the assembly and adjacent the first scissor return arm, wherein a portion of the first bushing extends into an opening formed in the first scissor return arm; a second bushing located on the opposite side of the assembly and adjacent the second scissor return arm, wherein a portion of the second bushing extends into an opening formed in the second scissor return arm; and a spacer pressed into both the first bushing and the second bushing such that the first and second scissor return arms are rotatably supported and captured by the first bushing and the second bushing.
 2. An assembly as set forth in claim 1, wherein the first bushing and the second bushing are generally identical.
 3. An assembly as set forth in claim 1, wherein the first bushing interlocks with the second bushing.
 4. An assembly as set forth in claim 1, further comprising a washer rotatably captured between the first and second scissor return arms.
 5. An assembly as set forth in claim 1, wherein the scissor return arms each comprise a first member that cooperates with a stop to establish a neutral position of the return to neutral mechanism, and a second member that is configured for the attachment of a biasing spring.
 6. A control mechanism for use with a hydraulic apparatus having a housing and a trunnion extending from the housing, the control mechanism comprising: a return arm rotatably mounted on the trunnion and attached to the housing, the return arm comprising a stop; a control arm attached to the trunnion; and a scissors arm assembly attached to the trunnion and biased to contact the stop to place the hydraulic apparatus in a neutral condition, the scissors arm assembly comprising a pair of scissor return arms, a first bushing located on one side of the scissors arm assembly wherein a portion of the first bushing extends into an opening formed in one of the scissor return arms, a second bushing located on the other side of the scissors arm assembly wherein a portion of the second bushing extends into an opening formed in the other of the scissor return arms, and a spacer pressed into the first and second bushings to form the scissors arm assembly and retain the pair of scissor return arms in relationship to one another.
 7. A control mechanism as set forth in claim 6, wherein the scissor return arms are biased to the neutral position by a spring attached to a portion of each scissor return arm.
 8. A control mechanism as set forth in claim 7, wherein the portion of the scissor return arm to which the spring is attached is angularly separated from the portion of the scissor return arm that contacts the stop.
 9. A control mechanism as set forth in claim 6, wherein the first bushing mechanically engages the second bushing.
 10. A control mechanism of claim 6, where the scissors arm assembly is rotatably mounted adjacent to the control arm on the opposite side of the control arm from the return arm.
 11. A control mechanism as set forth in claim 6, wherein the scissors arm assembly further comprises a washer rotatably captured between the pair of scissor return arms.
 12. A control mechanism as set forth in claim 11, wherein the first bushing and the second bushing are generally identical.
 13. A return to neutral mechanism for a hydraulic apparatus, comprising: a first scissor return assembly comprising a first arm and a second arm angularly separated from one another; a second scissor return assembly comprising a third arm and a fourth arm angularly separated from one another, wherein the first arm and the third arm interact with a stop to establish a neutral position for the hydraulic apparatus; a spring mounted on the second arm and the fourth arm to bias the first arm and the third arm toward the stop; a first bushing engaged to the first scissor return assembly; a second bushing engaged to the second scissor return assembly; and a spacer inserted into the first bushing and the second bushing to secure the first scissor return assembly to the second scissor return assembly in a manner whereby the first and second scissor return assemblies are permitted to rotate with respect to one another.
 14. A return to neutral mechanism as set forth in claim 13, wherein the first bushing and the second bushing are generally identical.
 15. A return to neutral mechanism as set forth in claim 13, wherein the first bushing interlocks with the second bushing.
 16. A return to neutral mechanism as set forth in claim 13, further comprising a washer rotatably captured between the first and second scissor return assemblies. 